(i) Electron deficient: The hydrides which do not have sufficient number of electrons to form normal covalent bonds is called electron deficient hydride.
For example, hydride of group 13 (BH3, AlH3, etc.).
(ii) Electron precise: The hydrides which have sufficient number of electrons required for forming covalent bonds is called electron precise hydride.
For example, hydrides of group 14 (CH4, SiH4, GeH4, SnH4, PbH4 etc.) they have tetrahedral geometry.
(iii) Electron rich hydrides: The hydrides which have excess electrons asrequired to form normal covalent bonds is called electron rich hydride.
For example, hydrides of group 15 to 17 (NH3, PH3, H2O, H2S, H2Se, H2Te, HF etc.)